Exclusive: Phil Davis, Gemma Jones join 'Merlin' cast

Phil Davis and Gemma Jones have signed up for guest roles in the upcoming fourth series of Merlin.

The BBC has confirmed exclusively to Digital Spy that former Spooks star Jones will appear in the new run's premiere episode.

She will play a mysterious character known as 'The Cailleach', described as the gatekeeper to the Spirit World.

Jones currently plays Madam Pomfrey in the Harry Potter films and recently starred in Woody Allen's You Will Meet a Tall Dark Stranger. The veteran actress also appeared in ITV's Trial & Retribution from 2003 to 2008.

Whitechapel star Davis will play the role of 'The Gleeman' in the third episode of Merlin's new series. An old world Circus-master, the character will arrive in Camelot to attend Prince Arthur's banquet, but is hiding a dark and sinister secret.

Davis's recent television credits include roles in Sherlock, Doctor Who and My Family. He has also appeared in such films as 2010's Brighton Rock and 2009's Dead Man Running.